Stroboscopic apparatus and method



Juneau, 1935.

P. DAvEY STROBOSCOPIC APPARATUS AND METHOD Original Filed Jan. 26, 1926 4A TToRNEYs.

Patented June 11, 1935 UNITED STATES PATENT OFFICE STROBO SCOPIC APPARATUS vAND METHOD Peter Davey, Mount Vernon, N. Y., assignor to Vibroscope, Inc., New York, N. Y., a corporation of New York A19 Claims.

My invention relates to thestroboscopic examination of moving bodies. Its primary object l is to provide apparatus, and also a method of operation, whereby Hash-illuminating stroboscopes can be made to produce sharp and Well dened images throughout a wide range of flashfrequencies, andespecially throughout a wide speed range, such as substantially throughout the whole range of machine speeds likely to be encountered in practice, say from 100 R. P. M. to 10,000 R. P. M. or more. This application is a division from my co-pending application Serial No. 83,984, led January 26, 1926.

'I-he accompanying drawing illustrates a preferred form of my4 invention. Figure 1 is a diagrammatic illustration of an entire stroboscope embodying the present'inventon. Figure 2 is a perspective of the interrupter unit thereof. Figure' 3 is a longitudinal section of the interrupter unit. Figure 4 is a section of the same on line IV-IV of Fig. 3; the line III- III indicates the section of Fig. 3. Figure 5 is a section on the line V-V of Fig. 3. Figure 6 is a conventional representation of discharges of an oscillating circuit, and Figure 7 is a diagrammatic illustration of another form of' the present invention.

The stroboscope in connection with which. the present invention is here illustrated comprises three separate units (Fig. 1), the illuminator A, the transformer or inductor unit B which provides the electric currents which light the illuminator, and the interrupter unit C which controls the time of lighting the illuminator. These three are united by flexible -leads long enough to permit the separate units to be disposed in convenient locations, that is to say, the unit B set down in operation in any convenient place, the interrupter C applied to a suitable driving shaft even though somewhat remote from the' unit B, and the illuminator approached close to the part to be examined independent of the location of B and C.

The illuminator A is an apparatus of the kind which is quickly lighted on the passage of an electric current and quickly darkened when the current ceases, such as a neon tube, in which tomarily mount this apparatus on a handle or holder with a suitable light reflector AI at one side of it so that the light can be conveniently (Cl. 176-124) approached to and directed on the particular moving part to be studied.

The transformer or induction coil which raises the voltage of the electric currents for the i1- luminator A is preferably contained in a case The transformer, it will be understood, transforms energy received from the source 20 into an electric current of suitable voltage to light the illuminator Whenever interrupter contacts I6 and I8 are actuated. In the present instance the core 'of the transformer is of iron, open magnetic circuit, and the primary circuit is of the closed circuitA type, energy being stored in the vcore of' the transformer in the form of magnetism created by. the current in the primary circuit when thecontacts I6 and I8 are closed, and being released to the secondary circuit arid illuminator when the contacts separate. In order to adapt the instrument to various shaft speeds, I have provided the primary winding of the transfer with taps as hereinafter explained and the multi-pole switch BI serving theseV taps is usually attached to the wall of the box so as to be accessible from the outside as indicated in Fig. 1. Ordinarily I use a battery 20 to supply the electric current to energize the transformer and this may be, included in the transformer case, but usually I place it outside and connect it to the circuits through binding posts located in the wall of the transformer box B as also diagrammatically indicated in Figure 1.

'Ihe interrupter unit C (outlined in Fig. l and shown in detail in Figs. 2 to 5) contains the contacts I6 and I8 in the circuit of the primary Winding of the transformer, and the interrupter shaft 6 which opens and closes them. The unit also embodies the adjustment features which permit the body under examination to be viewed in any position throughout its cycle, and mechanism'whereby the number of liashes per rotation of the shaft 6 can be varied at will. The head I of this unit has a central projecting cylindrical boss 2 on which a rotatable s1eeve` 3 is mounted; a cover Il extending from the periphery of the head I houses the various other mechanism, and a screw or screws 5 fastens the ,cover to the head. The shaft 6 projects from the enclosure of this cover through the boss 2 and a ball bearing 1 mounts the shaft in the sleeve 3. This bearing not only acts as a radial bearing, but also holds the shaft against endwise movement with respect to the sleeve. collar 8 on the shaft conceals the bearing and protects it from dirt. The sliaft 6 also has a radial bearing, rather long or extended, in the boss 2; this tends to reduce vibration, and within this long bearing a circumferential groove I0 is provided for lubrication purposes. On the outer end of the shaft 6 is a centering point II to be pressed against the end of a shaft (say of the machine under examination) which is rotating at such a speed as to produce the proper number of interruptions of the primary circuit as will be understood. The frictional engage ment 0f a centering point Il with the driving shaft is quite suflicient to drive the interrupter, and because of its simplicity and convenience this is a very desirable arrangement for driving stroboscopes, or at least for driving portable stroboscopes. The shaft 6 actuates the cont-.acts I6 and I8 by a cam I2 on its opposite end, which is arranged to strike a lever I5 carrying the contact I6 and which is so biassed by the spring AI'I as to hold the contact I6 in engagement with the stationary adjustable contact I8, except when lifted by the cam. Usually I place a block 2I on the lever to receive the blows of the cam or cams. The lever I5 and contact I8 are conveniently mounted on a plate I4 attached to the head I as shown, and as before indicated, rather long flexible conductors 34, entering the box B through the insulator 36h (Fig. 1), connect the contacts I6 and I8 to the primary winding of the transformer B and the source of energy 20 in series as shown in Fig. 1. 'I'he condenser to reduce the arcing or sparks at the contacts I6 and I8, appears at I9, and is connected in shunt to the contacts I6 and I8. I have found that it is important in flash-illuminating stroboscopes that this condenser be placed as close to the interrupter contacts as possible, and I therefore mount it in or as a part of the interrupter unit. It may be fixed to the plate I4 as shown in Fig. 3. The cam I2 lifts the contact I6 olf the contact I8 once in each rotation of the shaft 6 as will be apparent. Other cams may be put on the shaft 6 to cause the contacts I6 and I8 to open more than once, at will, in each rotation of the shaft. Another such cam is shown at I3, and this cam is shown as displaced angularly from the cam I 2 and also displaced from the cam I2 longitudinally of the shaft so that by adjustment either the cam I2 alone or both cams I2 and I3 may be made to strike the lever I5. Cam I3 therefore, by proper adjustment, in cooperation with cam I2 provides for interrupting the primary circuit twice in each shaft rotation and at opposite points in the cycle. To bring different cams into operative relation to a lever such as I5, I have found it important that the lever be mounted immovable axially and the cams be arranged for axial adjustment, rather than that the lever be mounted for axial adjustment on its fulcrum pin and the cams fixed axially as has been proposed heretofore. My construction produces a simpler motion of the lever and more reliable operation. I have therefore mounted the lever I5 in fixed axial position on the plate III and a ranged the shaft 6 to slide, carrying its cams 2 4and I3 with" it. To slide the shaft to the le t or right, the sleeve 3 is slid on the boss 2, and a ball or balls 22 pressed by springs 23 in the boss coact with two grooves 25 on the inner periphery of the sleeve Vto define the two positions of the shaft and frictionally hold the sleeve and shaft in each of these positions until manually moved at the will of the operator. When the shaft 6 is in its right hand position as shown in Fig. 3, only the cam I2 strikes the lever I5 as before described. When the shaft is moved to the left however (with respect to Fig. 3) the cam I3 is also brought into position to strike the block 2| and the latter being wide enough to be struck by the cam I2 when the shaft is to the left as Well as when it is to the right, the lever I5 is then actuated twice in each rotation of the shaft and the engagement of I6` with I8 is broken twice, bringing about two light flashes in the illuminator for each shaft rotation in the place of one when the shaft is in its right hand position. l

A second function of the balls 22 is to impose sufficient frictional resistance between sleeve 3 and the boss 2 to prevent the head I turning with the shaft. A pin 29, the inner end of which is flattened underneath the lever I5, can be turned at will by the nurled head 30 and when turned temporarily retains the contact I6 out of engagement with the contact I8; a sight plate 3|, fixed to turn with the pin 29 is exposed through a port 32 and conveniently marked, as

with Off and On, to indicate whether the contact I6 is held off the contact I8 or whether the instrument is in condition for operation. The same plate 3I may cooperate with pins 33 to restrict the turning movement of the pin 29 to the desired limits, while notches in the cover cooperating with a ball pressed by a spring 35 on the plate 3| (see Fig. 3) holds therpin frictionally in its two extreme positions. I

In operation, the coil case and battery (if any) are set down in any location convenient to the machine containing the part to be examined as before indicated. The centering point II of the interrupter unit is then pressed against the center of the end of a convenient shaft rotating at a `suitable speed relative to the frequency of the cyclic operation of they part to be examined (usually a shaft of the' machine being examined), so that the interrupter shaft 6 is driven, say, at the same speed as the shaft to which it is applied. What con-A stitutes a suitable speed for the machine shaft driving the interrupter shaft will be under- .stood by those skilled in this art, but for the purposes of this explanation will be assumed to be such a speed that the machine shaft makes one revolution while the part to be examined moves through one complete cycle. The

interrupter may be held againstthe machine shaft by hand, or clamped in place, the sleeve affording a convenient part for clamping purposes as will be apparent. In the alternative, a separate motor may'be used to drive the interrupter. With the interrupter shaft in its innermost or right and position as/shown in Fig. 3, the primary ,circuit of the transformer is Pinterrupted once during each otation of the interrupter shaft, each interru ion causing the induction of a train or'v group of voltage waves in the secondar'ycircuit which gradually decrease in value during the`period -in which the primary circuit is'opn. A train of such waves is conventionally shown by the curve 31 in Fig. 6. The apparatus is intended to be so designed that only one wave -or half cycle of voltage suflicient to light the illuminator.

each train is of sufficient amplitude to produce illuminating current in the illuminator A. The line 36 being the zero line, the broken lines 36a may be regarded as indicating the value of By this means therefore, the illuminator A produces a single and almost instantaneous flash of light each time the contacts I6 and I8 are operated and the rotations of the shaft B being synchronous with the cyclic movements of the part to beexamined, all these flashes occur at the same point in the cycle of the part being examined. When the illuminator A,- therefore is approached to and directed toward the moving part to be examined, this part is illuminated when, and only when, it is at some certain `point or stage ofits cycle and hence appears to the eye to be standing stationary at this point. To view the moving part in some point of its c ycle other than that in which it is first seen, the angular relation of the lever I5 to the shaft cam must be changed, which can be done with the greatest convenience by simply turning the cover 4 and thereby the head I. This makes the light flashes occur earlier or later in the cycle. The amount of this angular shift, or the difference in phase between any two certain positions of the moving part under.-

examination, can. be measured by thus turning the cover I with respect to the sleeve 3 and noting thereby the angular distance through which the lever I5 must be carried to change 'the View from one of these positions to the other. For this purpose, I usually provide a pointer 26 secured by a post 2l' to the' sleeve 3 in juxtaposition to ascale 28 marked circumferentially, usually lin degrees, on the cylindrical surface of the cover Il adjacent thereto. By pulling out the shaft 6 to its left hand position (or, contra, pulling the cover 4 and head to the right away from the,v sleeve 3), so las to bring cam I3 into action, the moving part vcan be viewed in two positions simultaneously, namely (because cams I2 and I3 are separated by at opposite points in its cycle. 'I'he moving part may be made to appear as though moving slowly, creeping, 'in its proper direction, by slightly releasing the pressure of the center point on the driving shaft so that a small degree of slipoccurs and the interrupter shaft 6 rotates slightly slower than the driving shaft. By driving the interrupter at a greater speed the moving part can be made to appear moving slowly backwards'.

A flash-illuminating stroboscope of the general type described (omitting referenceto the present invention) is subject to the limitation that it produces sharp and well defined images only within a limited range of speed; that is to say, if the instrument is designed for successful operation at low shaft speeds, then it f ails entirely at materially -higher shaft speeds; or if designed for high speeds,l then it produces poorly outlined images at materially lower speeds,`or even two or more images slightly displaced from each other where only one should be seen. This, I believe I have discovered, is due to the time-constant of the transformer and the varying periods of energization. That is to say, the inductance in the primary circuit delays the building up ofthe current in this circuit, so that it grows or only builds up slowly following each closing of the'primary circuit at the contacts I6 and I 8,' and its ultimate value depends on the length of time the contacts are held closed.

At slow'speeds the contacts are permitted to remain closed for longer periods than 'at high speed, and accordingly the primary currents reach higher values at low speeds than at high and hence energize the magnetic field more highly, i. e., produce a greater number of magnetic flux lines in it. Accordingly the voltages induced in the secondary winding vary inversely tothe speed. Assuming, for example, that the transformer is so constructed that the short closing-periods of the contacts at high speeds are long enough to build upthe magnetic field to a value capable of inducing a voltage wavetrain in the secondary winding having one wave of sufficient amplitude to light the illuminatbr A (i. e. greater than the voltage indicated lby the broken line 36a in Fig. 6 previously referred to), then at low speed, when the contacts II and I8v are allowed to remain closed for longer periods of time, the magnetic circuit is so much more highly energized that it induces wave trains, each of which has two or more waves or half cycles of suicient amplitude to'produce flashes in ythe illuminator, so that the resulting images are indistinctly outlined or multiple images are produced where only one should be seen. Contra, if the transformer is so constructed, that at low speeds the magnetic eld buildsup to a value only sufficient to induce one wave of sufcient amplitude to light the illuminator, then at high speeds (the windings being neither increased nor diminished and all other things remaining unchanged) the magnetic circuit is so incompletely energized during each short charging period that the resulting wave trains have no waves of sufficient amplitude to light the illuminator, and the apparatus fails entirely. To operate throughout a wide speed range therefore it is only necessary to compensate for the variations in the length of the periods in which the contacts are held closed (or the variations in the ratiotof contact-open periods to the contact-closed periods) to the end of maintaining the product of the number of effective or active turns in the secondary winding,-

without my invention may function quite satis-` factorily at a certain speed when producing one view per cycle, but fail when used to. produce two or more views per cycle at the same speed. Obviously the reverse is also true. My invention may be used to'correct for this also, as is quite apparent.

Preferably I compensate for changes in the periods ofthe contact operation which accompany changes in the frequency of operation. by counteracting the tendency for the maximum or ultimate strengths of the magnetic field to vary, specifically by vchanging the time-constant of the primary or inducing circuit inversely to the change of speed; more preferably by changing the inductance of the primary circuit, and more preferably still by reducing the inductance of the'primary circuit by cutting out transformer-primary turns when the speed is increased, and increasing the same inductance by cutting in turns when the speed is reduced, thus speeding up the creation of the magnetic i'leld with increasing speed andrdelaying the building up of the field as the speed is reduced, so that at every speed the magnetic circuit is energized suciently to light the illuminator Vbut at no speed is the 'eld energized suciently to produce two voltage Waves in a single train of sucient amplitude to light the illuminator. It is not necessary that the strength of th'e field bear a close relation to the speed, and/ this is especially true Where the discharge is highly damped, so that there is a wide diierence in amplitude between the maximum Wave and the next highest in the train. High damping in itself, it will be observed, broadens the range of speed (i. e., contact frequency) that can be covered-.without any change in the circuits or apparatus, inasmuch :as it permits considerable difference between the lowest speed which produces a train of waves 31 (Fig. 6) whose second highest Wave 38, for example, is lessv than 36 and hence is insuiiicient to light the illuminator, and the highest speed which produces a wave train 39 whose maximum wave is sufficient to light the illuminator.. I have found three or four adjustments of the number of primary turns are sufficient to cover the entire range of speed usually encountered in practice. The taps 40 and 4| in the Iprimary circuit of the transformer, in 4conjunction with the terminal connection 42 provide for three changes in the inducing circuit inductance. The tap switch BI with its movable switch arm is a convenient means for changing the connections to any one of thesek leads. For the highest speeds the magnetizing current is made to travel the tap 40 and hence only the smallest part of thel primary circuit. Accordingly the magnetic field is built up rapidly. For the lowest speeds the terminal connection .42 and the entire primary winding are utilized, and hence the magnetic iield is built up much more slowly. At some certain intermediate speeds the tap 4| and an intermediate part of the primary winding are resorted to s'o that the magnetic eld builds up at an intermediate rate. While the proper location of the higher speed taps in a winding satisfactory as a whole for low speed work, can be predetermined to some approximate degree as appears from the foregoing, the subject oi' induction coils and oscillating transformers of the type used in this work is so far from having been reduced to exact calculation, it will be understood, that the best-location of the taps may require experiment and trial on each size and type of apparatus. be understood that regardless of the correctness of my theories of the cause of the fault and its!l counteraction as' above explained, the fact is that taps such as 40, 4|, etc., suitable locations f It must also mary circuit.

magnetic field to any predetermined value varies of course, inversely with the value of the voltage applied to the primary Winding of the nductor at B. As an alternative therefore, the tendency for the eld strength to vary with the frequency of contact operation can be compensated for and counteracted by suitably varying the voltage of the source 20, using higher source voltages with the higher speeds and lower source voltages with lower speeds. The same result can be obtained without varying the source voltage, by adding ohmic resistance in series with the primary winding as the speed is increased and reducing the resistance of the primary circuit as the speed is reduced. The latter is illustrated in Fig. 7 wherein the box B with its transformer or induction coil, leads A2 and 34 and current source 20 of Fig. 1, will be recognized; in lieu of the switch B and primary winding taps of Fig. l, a manually-variable resistance B" is provided in series with the primary winding, the amount of the resistance element 5D in the primary circuit being variable at will by turning the pivoted lever 5|.

Furthermore the capacity of the condenser I9 affects the range of operations. ducing the capacity at this point as the speed is increased and increasing the capacity for reduced speeds, the range of operation of the instrument can be increased. This is not so desirable as the use ofthe tapped primary however, because the tapped primary operation entails a higher resistance in the primary circuit with the lower speeds and thus is more economical in battery consumption.

While I have thus describedwhat I believe to be the best forms of my invention, it will be understood that my invention is not limited thereto except as hereinafter .appears in the claims. Furthermore, it will be understood that my present invention is not limited to the particular stroboscopic apparatus illustrated and described; for the most part this particular stroboscopic apparatus is intended to be merely representative of the type of apparatus to which 2. In stroboscopic apparatus, the combination Aoi a dash-illuminator, an induction apparatus for supplying lighting currents thereto, contacts to open and close the primary circuit of said induction apparatus to produce lighting currents, and adjustable means connected to said primary circuit to change the time constant of said pri- 3. In stroboscopic apparatus, the combination of a ash-illuminator, an induction apparatus for supplying lighting currents thereto, contacts to ppenand close the primary .circuit of said induction apparatus to produce' Ylighting cur-V rents, and adjustable means to chan l.',the'value oi the currents producefd in said primary cir-` cuit `during theperiods when said contacts are closed.

By suitably re- 4. In stroboscopic apparatus, the combination-Jafof a' Hash-illuminator, an induction'apparatus for supplying lighting currents thereto, Acontacts to open and close thefprimary circuit of `saidinprimary circuit to carry 'primary-circuit current.

` which sharpnd Well defined images are pro-v 5. In stroboscopic apparatus, the combination of a flash-illuminator, an induction apparatus for supplying lighting currents thereto, contacts to open and close the primary circuit of said induction apparatus tol produce lighting currents, means providing current for said primary circuit, and an adjustable resistance con nected in series With said primary circuit and said means.

6. In stroboscopic apparatus, Athe combination of a/ilash-illuminator, an induction apparatus for supplying lighting currents thereto, contacts to open and close the primary circuit of said induction apparatus to produce lighting currents, means for providing current for said primary circuit, and adjustable means for varying the voltage-applied to the primary circuit by said current-providing means.

7. In stroboscopic apparatus, the combination of a flash-illuminator, an induction apparatus for supplying lighting currents thereto, contacts to open and close vthe primary circuit of said induction apparatus to produce lighting currents, condenser means connectedto said primary circuit, and adjustable means for changing the effective capacity of said condenser means.

8. In stroboscopic apparatus, the combination with a flash-illuminator, an induction apparatus for supplying lighting currents thereto, and contacts to close and open the primary circuit of said induction apparatus to produce lighting currents, of means for enlarging the range of frequencies of contact operations throughout duced, comprising means for compensating for the tendency of the product of the number of `said induction apparatus, of meansl for changing,

turns in the secondary' Winding of said induction apparatus,- multiplied by the rate of change ofthe inducing magnetic flux, to change with thefrequency of operation of the contacts.

, r9.1' In Vstroboscopic apparatus, the combination with a flash-illuminaton'an induction apparatus Yto provide lighting currents therefor, and controlling contacts in the primary circuit of the inductance of said primary circuit.

10. In stroboscopic apparatus, the combination of a flash-illuminator, anl induction apparatus having primary and secondary circuits to provide lighting currents therefor, and contacts to open and close the primary circuit ofA said induction apparatus, characterized by the fact that separate .taps are provided in the primary winding of said induction apparatus.A

11. The method of obtaining sharp and Well defined images, from a flash-illuminating stroboscopic apparatus, at ldifferent frequencies of flashes, Which consists in maintaining the product of the number of active secondary turns of the induction apparatus, multiplied by the number of magnetic iluxlines cutting the said secondary turns per unit of time, within such limits. that each induced voltage-trainhas one Wave, and substantially only one Wave, of suincient amplitude to light the illuminator.

12. The method of increasing the flash-frestroboscopic apparatus, which consists in maintaining, throughout the range of operations, the product of the number of active secondary turns of its' induction apparatus, multiplied by the number of magnetic flux lines cutting the said secondary turns per unit of time, Within such limits that each induced Voltage train has one Wave, and-substantially only one Wave, of suicient amplitude to light the illuminator.

13. The method of obtaining sharp and Well defined images, from a flash-illuminating stroboscopic apparatus, throughout a range of flash frequencies, which consists in counteracting the tendency of the product of the number of active secondary turns in the inducing apparatus, multiplied by the rate of change of the magnetic flux thereof, to change with the frequency of the flashes.

14. The method of obtaining sharp and well defined images, from a flash-illuminating stroboscopic apparatus, throughout a range of flash frequencies, which consists in restraining the inherent tendency of the strength of the inducing magnetic field to Vary with the frequency of the flashes. v

15. The method of increasing the flash-frequency range throughout which a flash-illumiquency range of operation of flash-illuminating i nating stroboscopicA apparatus produces sharp and well-defined images which consists in counteracting the -inherent tendency of the strength of the inducing magnetic field to vary with the frequency of the flashes, thereby maintaining the strength of the magnetic field, throughout the range, Within limits suited to produce a single voltage Wave, and substantially only a single voltage Wave, at each operation of the contacts, of sufficient amplitude to light the illuminator.

16. The method of enlarging the range of flash-frequencies throughout which a flashilluminating stroboscopic apparatus produces sharp and Well defined images, Which consists in changing the time-constant of a circuit of the inducing apparatus in a direction to comf pensate for changes in the periods of the operation of the controlling contacts which accompanics changes in the frequencies of the flashes.

17. The method of operating flash-illuminating stroboscopic apparatus to increase the flashfrequency range of operations, which consistsin changing the value of the time-constant of the inducing circuit of the induction apparatus, inv a direction inverse to the change in the frequency of the flashes.'

18. The method of operating flash-illuminatingstroboscopic apparatus which consists in changing the inductance of the primary circuit of the induction apparatus in a direction inverse to the change in the frequency of the flashes. i i

19. The method of increasing the range of flash-frequencies of a flash-illuminating stroboscopic apparatus, which consists in reducing the number of active primary inducing turns in the of active turns of said Winding when the f re` quency of the flashes is reduced.

PETER DAVEY. 

